Tricyclic overdose with a wide QRS and shock refractory to bicarbonate

Immediate therapy: sodium bicarbonate 8.4% (1 mEq/mL), 1–2 mEq/kg (roughly 100–150 mEq) as a slow intravenous push over one to two minutes, repeated every few minutes until the QRS narrows and the arterial pH is 7.45–7.55. Then start an infusion of 150 mEq in 1 L of 5% dextrose at about twice maintenance rate, with hourly blood gases and continuous rhythm monitoring.

The physiology. Amitriptyline blocks the fast inward sodium current in the His-Purkinje system, slowing phase 0 depolarisation and widening the QRS; it also blocks norepinephrine reuptake, producing a catecholamine-excess state with hypotension and arrhythmia. Bicarbonate works by two mechanisms: it delivers a sodium load that overcomes the competitive channel block, and it alkalinises plasma, which increases protein binding of the tricyclic and reduces the free, active fraction. The QRS width and the arterial pH are the bedside end-points, not the serum level.

Avoid 1: flumazenil and physostigmine. Both lower the seizure threshold, and in a pro-convulsant overdose the seizure is the lethal event - it produces acidosis, which liberates more free drug and widens the QRS further.

Avoid 2: class IA, IC and III antiarrhythmics (procainamide, flecainide, amiodarone, sotalol). They further block sodium channels or prolong repolarisation. A wide-complex tachycardia in this setting is treated with bicarbonate, not with an antiarrhythmic. For the same reason, avoid phenytoin, and use benzodiazepines for seizures.

Also on the list: activated charcoal 1 g/kg only if the airway is protected and ingestion is under one to two hours; no gastric lavage; treat hypotension with norepinephrine rather than dopamine.

Step 1 - vasopressor. Start noradrenaline peripherally or centrally and titrate to a MAP of at least 65 mmHg. Noradrenaline is the right first agent because the circulation is vasodilated and the myocardium is sodium-channel poisoned; dopamine is more arrhythmogenic. Correct potassium, magnesium and calcium, and check the arterial pH after each bolus.

Step 2 - continue bicarbonate to the pH and QRS end-points rather than abandoning it because the pressure has not yet responded; there is often a lag.

Step 3 - 20% lipid emulsion as a rescue, 1.5 mL/kg (about 100 mL) over one minute, then 0.25 mL/kg/min for 30–60 minutes. It creates an intravascular lipid phase that sequesters lipophilic drug and may also support myocardial fatty-acid metabolism. The evidence in tricyclic overdose is weak and it is a rescue therapy, so it must not displace vasopressors, bicarbonate or the ECMO conversation.

Step 4 - define the failure point now, not later. In a two-hour-transfer system, the decision to move has to precede the arrest. I would call the ECMO centre for advice as soon as the patient needed a second bicarbonate bolus with vasopressors, and I would use these triggers to activate retrieval: persistent shock despite bicarbonate plus noradrenaline plus lipid; a QRS that fails to narrow; recurrent ventricular arrhythmia; pH below 7.0 with rising lactate; or cardiac arrest with ongoing CPR. Retrieval of a perfusing patient is feasible; retrieval of a patient in refractory arrest, two hours away, is usually not.

Intubation is a decision in its own right. If he needs it, pre-oxygenate, use ketamine and rocuronium, avoid propofol in a hypotensive patient, and expect post-intubation collapse - have vasopressors running before induction. Avoid hyperventilation as a substitute for bicarbonate: it produces alkalosis without the sodium load.

Disposition. He is close to medical clearance but not yet clear. After a significant tricyclic ingestion he needs continuous cardiac monitoring for at least six hours beyond the point at which the QRS, the pH and the level of consciousness are all normal, with serial observations and no access to his belongings. If he remains well at that point, and a repeat ECG shows a normal QRS and QT, and the blood gas is normal, he can be medically cleared for psychiatric assessment.

He cannot go home. He has taken a deliberate overdose with suicidal intent; a 30-hour wait for a psychiatric bed means he stays in the emergency department under one-to-one observation, in a ligature-risk area, with a documented mental state examination and capacity assessment. I would contact the on-call psychiatrist to arrange urgent review rather than an outpatient referral, and I would use mental health legislation if he tries to leave.

What would make me keep him:

• Any recurrence of QRS widening, a new arrhythmia, or a fall in pH - these indicate ongoing sodium-channel toxicity and reset the observation clock.
• Hypotension needing vasopressors, or a seizure - either mandates critical care, not a ward.
• Uncertainty about co-ingestion: I would send a paracetamol level, check the ECG for a long QT suggesting another agent, and screen for alcohol, benzodiazepines and opioids.
• Aspiration, drowsiness with an unprotected airway, or a rising lactate.
• A change in mental state that suggests an alternative diagnosis such as hypoxia, hypoglycaemia or head injury.

Documentation. Record the ECG parameters at each time point, the drugs and doses given, the peak QRS, the discussions with psychiatry, and the exact observation level he requires. Also ask about the argument, and offer him a chance to talk - the underlying crisis does not go away when the QRS narrows.